Adenocarcinoma of the prostate is the most common cancer of adult males in the United States. Of the patients diagnosed with this malignancy each year, over one half have locally advanced or metastatic disease at the time of diagnosis.While it is generally accepted that the growth and differentiation of benign and malignant prostatic epithelium is regulated by androgens, epidemiologic evidence suggests that 1alpha-25(OH)2 vitamin D3 [1alpha, 25(OH)2D3] may also play a role in prostatic carcinoma progression. The investigators have recently discovered that in addition to androgen receptors, human prostatic carcinoma cells also contain specific, high affinity receptors for 1,25(OH)2D3. The preliminary studies by the investigators using LNCaP cells have revealed that 1,25(OH)2D3 is capable of regulating growth (cell number), and prostate specific antigen production in a dose dependent fashion. The proposal outlines the rationale and methods to further test the hypothesis that receptors for vitamin D metabolites can modulate the growth and/or differentiation of human prostatic carcinoma cells in vitro and/or in vivo. A variety of human prostatic carcinoma cell lines including LNCaP, PC-3, DU 145, ALVA 31, PPC-1, TSU-PR1 and JCA-1 will be examined. Vitamin D receptors in these cells will be characterized by competitive binding, sucrose gradient sedimentation, DNA affinity chromatography and Western blot analysis. Metabolism of 1,25(OH)2D3 in vitro will be assessed using high pressure liquid chromatography and/or gas chromatography/mass spectrometry. Regulation of vitamin D, androgen and epidermal growth factor receptor expression will be assessed using competitive binding and/or Northern blots. Phenotypic differentiation will be assayed using radioimmunometric assays of prostate- specific antigen (PSA) and/or prostate specific acid phosphatase. Analysis of PSA mRNA synthesis will be assessed by Northern and slot blot assay. The results obtained with continuous carcinoma cell lines will be compared to those obtained with primary cultures of benign and/or malignant prostatic epithelial cells. Finally, the effects of vitamin D deficiency or excess will be evaluated in vivo using xenografts to nude mice or nude rats.